1. Field of the Invention
The present invention relates to an apparatus for reducing nitrogen oxide of exhaust gas, and more particularly to an apparatus for reducing nitrogen oxide for mixing urea with the nitrogen oxide so that the purification rate of the nitrogen oxide in the exhaust gas can be improved.
2. Description of Related Art
Generally, exhaust gas that is exhausted through the exhaust manifold of an engine is induced to pass through a catalytic converter that is mounted in the middle of an exhaust pipe to be purified, and the noise thereof is reduced while passing through a muffler and the exhaust gas is discharged to the outside through a tail pipe. The catalytic converter is a type of soot filtering device or diesel particulate filter (DPF) to process the pollution materials that are included in the exhaust gas. And, a catalyst support is formed inside the catalyst converter to filter the particulate materials that are included in the exhaust gas and to purify the exhaust gas that is exhausted from the engine through a chemical reaction.
One of the catalysts that are applied to the catalyst converter that functions as above is a selective catalyst reduction apparatus (SCR). Reducing agents such as carbon monoxide, total hydrocarbon (THC), and so on react well with nitrogen oxide rather than oxygen in the selective catalyst reduction apparatus (SCR), so it is called a selective catalyst reduction apparatus (SCR). Among the selective catalyst reducing apparatuses, the ammonia-SCR uses ammonia as a reducing agent to purify the nitrogen oxide, has good selectiveness to the NO, and has a merit in which it reacts well with the NO in the presence of oxygen.
The urea-SCR that is applied in a vehicle like the ammonia-SCR also selectively eliminates nitrogen oxide. The urea-SCR injects an aqueous solution of the urea at an upstream side of the catalyst and uses ammonia that is transformed from the injected urea to selectively reduce the nitrogen oxide, so it is called a urea-SCR.
In the urea-SCR, when the injection amount of the urea is increased, the purification rate of the nitrogen oxide can be increased. However, when the urea is injected more than normal, remaining urea that does not react with the nitrogen oxide is transformed to ammonia. Accordingly, it is very important to optimize the injection amount of the urea and to simultaneously improve the purification rate of the nitrogen oxide in the urea-SCR.
The injected urea is to be uniformly mixed with the exhaust gas so as to enhance the purification rate of the nitrogen oxide, and the length of the exhaust apparatus needs to be lengthened so as to improve the mixing rate of the urea and the exhaust gas. However, the exhaust apparatus of the vehicle is set at a predetermined length, so the urea and the exhaust gas cannot be uniformly mixed to flow into the urea-SCR such that the purification efficiency of the nitrogen oxide is reduced. Also, the ammonia that remains by not reacting with the nitrogen oxide is discharged to the outside and causes an offensive order from the exhaust gas.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.